1. Field of the Invention
This invention relates to a swivel joint for connecting fluid pipes.
2. Description of the Prior Art
There is known a submarine petrolem production system moored at a single point and floating on the surface of the sea in the vicinity of a submarine oil or gas field. The system includes an apparatus for the storage and primary treatment of petroleum or natural gas arriving from the field at the bottom of the sea and a loading and unloading apparatus. The system also includes a plurality of pipelines for transporting petroleum or natural gas having a high temperature and a high pressure from a plurality of pits at the bottom of the sea to the storage apparatus and a plurality of pipelines for supplying a high pressure fluid for service or injection purposes from the treating apparatus to the pits. The system floating on the surface of the sea is caused to swivel about the mooring device by waves, wind and tides. A swivel joint is, therefore, provided at the swiveling center of the system for connecting the pipelines.
A typical swivel joint known in the art is shown in FIGS. 5 and 6. It comprises a plurality of elements 01. Each element 01 comprises a cylindrical rotatable portion 02, a cylindrical stationary portion 03 and a rolling contact bearing 06 which supports the rotatable portion 02 rotatably on the stationary portion 03. The bearing 06 can bear the radial and axial loads. The rotatable and stationary portions 02 and 03 define an annular fluid passage or chamber 04 therebetween. A sealing member 05 is provided between the rotatable and stationary portions 02 and 03. The two elements 01 shown in FIG. 5 are connected one upon the other. The upper element 01 has a fluid inlet 07 and a fluid outlet 08 between which the fluid respective passage 04 extends. Likewise, the lower element 01 has a fluid inlet 07' and a fluid outlet 08' between which the respective fluid passage 04 extends.
The known swivel joint has the following drawbacks that are due to the use of the rolling contact bearings 06:
(1) The rotatable and stationary portions 02 and 03 are heated by the hot fluid flowing through the fluid passage 04. They are thermally expanded and increase their diameters. The bearing 06 is, however, an accurately finished product. If the clearance between the races increases as a result of thermal expansion, the load acting on the bearing 06 is concentrated on some of the rollers and causes them to fracture.
(2) The bearing 06 can bear only the radial and axial loads. It does not respond to the upset moment which is generated when a horizontal load has acted upon the rotatable portion 02.